The reflexive Banach space fixed point property conjecture

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Let XX be a Banach space. It has the fixed point property for nonexpansive mappings when every nonempty closed, convex and bounded subset C⊂XC\subset X and every map T ⁣:C→CT\colon C\to C satisfying

∥T(x)−T(y)∥≤∥x−y∥\|T(x)-T(y)\|\leq\|x-y\|

for all x,y∈Cx,y\in C has a fixed point in CC.

Reflexive-space fixed point conjecture. Every reflexive Banach space has the fixed point property for nonexpansive maps. Equivalently, if XX is reflexive and C⊂XC\subset X is closed, bounded and convex, then every nonexpansive self-map T ⁣:C→CT\colon C\to C has a fixed point.

Reflexivity guarantees weak compactness of bounded subsets, but known fixed point theorems generally require additional hypotheses such as uniform convexity or normal structure. Nonreflexive examples exist both with and without the property, while the existence of a reflexive Banach space failing the fixed point property remains open.

References

Primary source

Faruk Alpay and Hamdi Alakkad, “On the Fixed Point Property in Reflexive Banach Spaces”, arXiv:2509.13121 (2025).

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Solutions 1

RemarkAI-assistedClaimed by OpenAI. Claims the fixed-point property in the given norm for every real reflexive Banach space: every nonexpansive selfmap of a nonempty closed bounded convex subset has a fixed point.See full solutionHide full solution

Claimed by OpenAI. Claims the fixed-point property in the given norm for every real reflexive Banach space: every nonexpansive selfmap of a nonempty closed bounded convex subset has a fixed point.

Scope relative to this problem: The source claims the fixed-point property in the given norm of every real reflexive Banach space, for nonexpansive selfmaps of every nonempty closed bounded convex subset. This retains the source real-scalar convention and does not change the assertion to existence of an equivalent norm or to group-action fixed-point properties.

GitHub repository: https://github.com/openai/math

Manuscript: https://github.com/openai/math/blob/adc7f1241b42e322a6451854ab7e4b4c146bf78a/preprints/Fixed-Points-of-Nonexpansive-Maps-in-Reflexive-Banach-Spaces-September-24-2026/paper.pdf

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